CAIRO — Egypt’s powerful spy chief under deposed President Hosni Mubarak roiled the country’s presidential race Friday by announcing his candidacy and presenting himself as the best choice for restoring security and prosperity.

Omar Suleiman’s announcement was widely seen as a game changer in the landmark election scheduled for next month. The prospect of his return to power would have been laughable a year ago, when he vanished from public view after somberly announcing that the country’s longtime autocratic ruler was stepping down.

But much has changed since that afternoon of Feb. 11, 2011. Islamists have thrived in the country’s newly open political system, alarming secular Egyptians and Western nations that would like to see non-Islamists leading Egypt. In addition, a large segment of Egyptian society has come to yearn for the safety and relative prosperity that prevailed until the popular uprising sent the economy into a tailspin and eroded the pillars of the country’s police state.

Suleiman’s candidacy broadens a field of front-runners dominated by Islamists. Political analysts said his entry, coming just days after he publicly ruled out a presidential bid, suggests that the ruling military council opted to anoint him as a contender, possibly in response to the Muslim Brotherhood’s decision to field a candidate and robust support for more hard-line Islamist candidates. It offers Egyptians their clearest choice yet between the old order and the new: a contender who is an old hand of the Mubarak-era security establishment facing off against Islamists who were banned from politics under the government he served.

“It just became a more interesting race, because it has become increasingly clear the regime has not collapsed,” said Khaled Fahmy, chairman of the history department at the American University in Cairo. “This represents the realization that the standoff with Islamists in parliament is very serious to them.”

Suleiman, a former army general, has remained largely invisible since the final days of Mubarak’s rule, during which he served briefly as vice president. Unlike the ousted president and several of his senior loyalists, Suleiman has not been put on trial, and the ruling military council has shown no sign of wanting to hold him to account for any of the abuses of the old government.

The former spy master was among Washington’s closest backers in the Middle East in recent years, championing Egypt’s unpopular alliance with neighboring Israel. The agency he ran played a key role in the rendition of U.S. terrorism suspects, a program in which suspects were secretly flown to countries around the world for interrogation after the Sept. 11, 2001, attacks, according to leaked diplomatic cables and news reports.

Suleiman announced his decision to run for president in a statement published Friday afternoon on the Web site of the state-run newspaper al-Ahram. He attributed his change of heart to a mass show of support at a rally in the Abbasiya district of Cairo earlier in the day.

“I was touched by your strong stance and your insistence on changing the status quo,” Suleiman’s statement said. He added that he was running in response to Egyptians’ desire for “security, stability and prosperity.”

Shadi Hamid, an Egypt expert at the Brookings Doha Center, said Suleiman could emerge as a strong candidate if the military council, which continues to command widespread backing, manages to galvanize support for the former Mubarak loyalist among pro-military Egyptians and those wary of the prospect of a fundamentalist leader.

“He’ll have a chance of winning if SCAF puts its weight around the candidate,” Hamid said, referring to the Supreme Council of the Armed Forces. “We’ll have to wait and see how much coordination there is between Suleiman and SCAF.”

If his candidacy was, in fact, engineered by the country’s military chiefs, the move could prove a risky gamble, opening up a once-shadowy figure to close scrutiny.

“I’m excited because now all the atrocities he committed over the years will be under the spotlight for the next two months,” said Hossam Bahgat, a prominent human rights activist. “He is the only member of Mubarak’s close circle who has not only not been indicted, but is not even being questioned over anything.”

To get on the ballot for the May 24 vote, Suleiman, 75, must gather 30,000 signatures or secure an endorsement from 30 lawmakers by Sunday, the deadline to register.

The announcement marked the latest surprise in a presidential race that a year ago had just three presumed front-runners: well-known former Egyptian diplomats Amr Moussa and Mohamed ElBaradei; and Abdel Moneim Aboul Fotouh, a moderate Islamist.

ElBaradei dropped out, and two prominent Islamists — the Muslim Brotherhood’s Khairat el-Shater and Hazem Abu Ismail, who enjoys the support of many in Egypt’s conservative Salafist community — emerged as credible rivals.

An opinion poll released this month by the al-Ahram Center for Political and Strategic Studies — which didn’t list Shater or Suleiman — has Moussa, the former head of the Arab League, in the lead with the support of 31 percent of the 1,200 Egyptians polled. Ismail ranked second, with the backing of 10 percent. Ismail is fighting to stay in the race amid allegations that his late mother was a U.S. citizen, which under Egyptian law would bar him from the country’s highest office.

Thousands of Ismail’s supporters thronged Tahrir Square after Friday prayers to demand that he be allowed to stay on the ballot. Many in the crowd said they saw Washington’s hand in the attempt to disqualify him.

“America is the number one player in what is happening in Egypt right now,” said Mohammed Hamdi, 45, an accountant who supports Ismail. “America wants a president under its wings that abides by its orders.”